#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>
#include<limits>
#include<iterator>

#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ll, char> plc;

int main()
{
	ll b1, b2, b3;
	cin >> b1 >> b2 >> b3;

	double r = (double(b3-b2)/(b2 - b1));
	double d = b2 - r*b1;

	printf("%lld\n",(ll)(round(r*b3 + d)));
	return 0;
}